<style>
    body {
      height: 2000px;
    }
    .banner {
      width: 100%;
      /*固定定位在浏览器左边的最底部*/
      position: fixed;
      bottom: 0;
      left: 0;
      /*横幅中内容水平垂直居中显示 */
      display: flex;
      align-items: center;
      justify-content: center;
      background-color: pink;
    }
    .banner-content {
      /* 自适应缩放 相当于 flex-shrink: 1;flex-grow: 1; flex-basis: 0; */
      flex: 1;
      min-height: 100px; /*最小高度*/
    }
  </style>
  <body>
    <div class="banner">
      <div class="banner-content">......</div>
      <!-- 关闭按扭可以加下面,关闭按扭不会写，看前面第8个案例 -->
      <div class="close-button"></div>
    </div>
  </body>